The present invention relates to a rolled copper or copper-alloy foil provided with a roughened surface. In particular, the present invention relates to a rolled copper or copper-alloy foil having fewer craters (which are failures in the roughening treatment caused by inclusions present at a surface layer of the copper foil), having good adhesive strength with a resin layer, having acid resistance and tin plating solution resistance, having high peel strength, having good etchability and glossiness, and suitable for manufacturing a flexible printed circuit board in which wiring can be finely patterned.
In recent years, due to advances in micro integration technologies for on-board components such as semiconductor devices and various electronic chip components, finer patterned wiring is increasingly demanded for printed wiring boards prepared from flexible printed circuit boards to mount those components.
Conventionally, an electrolytic copper foil subjected to roughening treatment to improve adhesiveness with resin has been used. However, this roughening treatment significantly impairs the etchability of the copper foil, leading to difficulty in etching at a high aspect ratio, and resulting in the occurrence of undercutting upon etching. These have posed a problem that sufficient fine pattern formation can not be achieved.
Accordingly, in order to control the occurrence of undercutting upon etching and satisfy the demand of fine pattern formation, lightly performing the roughening treatment of an electrolytic copper foil, that is, low profiling (reduced roughness) has been proposed.
However, low profiling treatment of an electrolytic copper foil has a problem that the adhesion strength between the electrolytic copper foil and an insulating polyimide layer is reduced. However, for this reason, desired adhesive strength can not be maintained, causing a problem that wiring falls off from the polyimide layer during processing while a high level of fine pattern formation has been demanded.
To solve the above problem, proposed is a method comprising: forming a thin zinc-based metal layer on an electrolytic copper foil having a non-roughened surface; and further forming a polyimide-based resin layer thereon (for example, see Patent Document 1).
Further, proposed is a technology in which a phosphorus-containing nickel plating layer is formed on an electrolytic copper foil in order to prevent undercutting (for example, see Patent Document 2). However, in this case, the surface of the electrolytic copper foil is required to be roughened or at least can be roughened. Furthermore, all of Examples in Patent Document 2 involve the formation of a phosphorus-containing nickel plating layer on a roughened surface of an electrolytic copper foil.
Nonetheless, with regard to properties required for a high level of fine pattern formation on a copper foil, problems are not limited to undercutting upon etching and adhesiveness with resin as described above. For example, strength, acid resistance, tin plating solution resistance, glossiness and the like are required to be excellent.
However, in the conventional technologies, these overall problems are not addressed, and currently, an appropriate copper foil capable of solving these problems is not found.
In this context, a pure copper-based rolled copper foil having high strength has been used in order to solve the problems in an electrolytic copper foil as described above.
In general, known is a copper foil in which a common pure copper-based rolled copper foil is further subjected to fine copper plating (so-called “copper nodule treatment of red color”) to improve the adhesion strength with resin or the like.
Usually, alloy plating of copper and cobalt or ternary alloy plating of copper, cobalt and nickel is further formed on this roughened surface to give a copper foil for printed circuits (see Patent Document 3 and Patent Document 4).
Recently, alternative to these conventional rolled copper foils, proposed is a rolled copper-alloy foil having further improved strength and corrosion resistance by which wiring can be finely patterned.
However, in a case where such a copper alloy rolled copper foil is plated with copper to form fine copper grains, a fault called a crater has occurred. This crater refers to a region of treatment failure (a spot), in other words, a non-treated fault in which copper grains are not formed or sparsely formed.
Note that the crater has an area of about 10 to 50 μm2 and an average diameter of about 3 to 10 μm. The term “crater(s)” as used herein is used in this meaning.
Accordingly, by improving plating treatment, the present applicants have proposed a rolled copper-alloy foil having 10 craters per 25 mm2 on a roughened surface of the rolled copper-alloy foil that was subjected to roughening treatment with copper fine grains (see Patent Document 5 shown below). In the above technology, which has been a very effective, the development of craters has been still observed albeit a small amount.
Patent Document 1: Japanese Patent Laid-Open No. 2002-217507
Patent Document 2: Japanese Patent Laid-Open No. S56-155592
Patent Document 3: Japanese Patent Publication No. H6-50794
Patent Document 4: Japanese Patent Publication No. H6-50795
Patent Document 5: Japanese Patent Laid-Open No. 2005-290521